Good questions there...

I have tried several ways to use the pots for tuning, but for me, that is not really the way. Others may have more luck with that, but personally, when tuning, I have the fuel curve open on screen, and adapt the curve as necessary.
What I do, is program two curves, on two separate receiver outputs.Each curve has as many points as there are index markers next to your throttle stick (most radios have index marks on the gymbals, if not, they are easy to make yourself).
One curve controls the throttle servo. This curve is NOT linear, but fairly progressive, such that at midstick, the throttle barrel of the carb is approx 1/4 to 1/3rd open.
The other controls the solenoid.
The throttle curve is a one time affair, I usually do not touch it once set.
Since each point on the curve corresponds with an index mark on the throttle gymbal, it is very easy to see, at which point you need to act

Normally, I start out with the fuel curve set at full fuel all across the entire range.
I open the main needle 1 turn, and with the throttle slightly above idle, I prime the fuel line so fuel is all the way in the tubing up to entering the carb. Then I close the needle again.
Now I apply the starter (best is to ask a helper to do this) and gradually open the needle until the engine runs.
Once the engine is running, make it a bit rich on the needle to create a bit of headroom, and then I increase throttle a bit until the engine leans out. In this stage, ignore indexes, curve points etc etc.
Repeat this opening of the needle then opening the throttle, until you have full throttle and a slightly rich engine. Do not touch the main needle after this anymore
Now comes the actual tuning of the curve.
Since you are at full throttle, the higherst point of the fuel curve is what you are operating at. Tune this point until you hear the engine leaning out again. For now no need to go "optimal", you just want to confirm that the set-up is responding to adjustments, and anyway, the engine was only slightly rich to begin with, so...
Then reduce throttle to the second highest index mark on the gymbal. Since the rest of the curve is still full open, the engine should immediately and noticably be fattening up.
Adjust this 2nd highest point on the curve, and work your way down all the way to idle.
Most likely, you will notice that below midstick, the fuel curve gets very low and becomes "coarse" (going from lich to lean in a single increment) and this is undesirable.
When this happens, first raise the curve again at that point, and act on the idle needle until you notice that the engine responds on that idle needle.
Then return to the method of pulling down throttle one index and adjusting the fuel curve.

It might be necessary to go back up and down the range several times, it might be necessary to act slightly on the idle needle a bit to find the optimal settings.

MInd you, this IS a bit of an aquired skill, so do not give up too quickly. I had to figure out this procedure all by myself since there was no one before me, and I managed. I am not a gifted person WRT tuning, and I figured it out as well.
The biggest issue, is that gasoline and spark, the AUDIBLE response of the engine to mixture changes is different than that of glow engines. You most definitely have to get used to that too.
There is no way around that, but trust me: once you picked up this skill, and grasp the principle behind the method above, it becomes really easy.
My first engines took me several hours to get halfway decent, but nowadays it takes about the time it took me to type this message...
Once you have a clean running curve, tune your main needle one click rich (or as much as needed to get an audible response) and go flying.
Give the engine a few flights before you start finetuning, and then use the following method:

Fly at a constant throttle setting, take note of which index you are at. carefully observe whether you think it needs adjustment or not. If so, LAND the plane, and adjust ONLY THAT POINT on the curve, by minute increments, and test again. If you are happy with it, test the next index point.
For fourstrokes: It is best, to do not more than one correction per flight, because the engine has to "get used" to every change.
This, because when you change mixture, it also affects the properties of the oil below the piston, but these properties follow with a very significant time delay. So whenever you change a setting, 15 minutes later the oil has stabilized and this affects internal drag in the engine, and thus RPM for that particular throttle setting.
State of break in also has an effect: brand new engines, depending on brand, are sometimes pretty inconsistent. ASP/Magnum/SC were particularly notorious for this, I have seen engines that needed an entire season of flying before they settled down on a consistent fuel curve.
I run predominantly ASP engines, and I can assure, they ALL settle down sooner or later, and even those cheap chinese OS copies eventually become very consistent and reliable.